A nuclear reactor is a device designed to gradually discharge a large amount of energy that is instantaneously emitted due to a mass defect occurring during nuclear fission of a nuclear fuel, thereby enabling nuclear energy to be applied to real life.
FIG. 1 is a cross-sectional view of a conventional nuclear reactor and a control rod driver.
A fuel assembly 2 is accommodated in the nuclear reactor 1. An assembly of a control rod 3 and a control rod driver attaching nozzle 4 that are configured to adjust the number of neutrons absorbed by nuclear fuel so as to control the combustion of the nuclear fuel, and a plurality of control rod driver 5 including control rod driving motors are installed on upper part of the nuclear reactor 1. The control rod 3 is vertically driven by the control rod driver 5.
The control rod driver is operated by a current signal flowing through four control rod driving coils, i.e., an upper lift coil (UL), an upper gripper coil (UG), a lower lift coil (LL), and a lower gripper coil (LG), and are configured to control the vertical movement of the control rod 3 by controlling motor driving using an electromagnetic force generated by power supplied to cables of the control rod driving coils.
The control rod driving coils used in the control rod driver 5 are required to have heat resistance so that the control rod driving coils may be prevented from deteriorating due to continuous operations of the control rod driver 5 during an automatic load follow operation. However, since coil wires are conventionally covered with an enamel-based insulating material, the coils deteriorate at a temperature that is higher than 220° C. to stop electricity generation. Thus, power generation is stopped until the system is re-operated, electric current is conducted through the coils due to the deterioration of and damage to the coils, and insulation breakdown thus occurs, causing the fall of the control rod and thereby degrading safety and reliability.